The Use of Dinoflagellates and Acritarchs for Zonation and Correlation of the Navarro Group (Maestrichtian) of Texas
James B. Zaitzeff, Aureal T. Cross, 1970. "The Use of Dinoflagellates and Acritarchs for Zonation and Correlation of the Navarro Group (Maestrichtian) of Texas", Symposium on Palynology of the Late Cretaceous and Early Tertiary, Robert M. Kosanke, Aureal T. Cross
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Eighty-one species of dinoflagellates and acritarchs have been identified from two sections of the Navarro Group in Texas. Forty-one species were distinguished from the Olmos and Escondido Formations from a 1170-foot core section in Frio County. Nearly all of those species and more than 30 additional taxa were identified from surface sections of the Neylandville Marl-Nacatoch Sand, Corsicana Marl, and Kemp Clay composited from several localities near Austin. The ranges of 56 of these entities are plotted to show zonation of the Navarro Group into three parts and tentative correlation of the Austin and Frio County sections. Twenty species found in the Neylandville-Nacatoch rocks near Austin were not found in the Frio County section, indicating that the base of the Navarro in Frio County is younger than the lower part of the Navarro in the Austin area, probably about early middle Corsicanan in age. An unconformity is demonstrated at the top of the Neylandville Marl-Nacatoch Sand in the Austin sections by the termination of range of these 20 species and by the first appearance of 15 additional species in the lowermost Corsicana beds. The ranges of nine forms terminate at approximately the position of the base of the Kemp Clay, to mark the base of the upper of the three acritarch-dinoflagellate zones.
The termination of range, in this area, of Palaeohystrichophora infusorioides and the peak development of five other species at successively younger time-correlative levels in both sections furnish a basis for further subdivision of the Navarro and time-line correlations between the two sections about 135 miles apart.
Pollen-spore/microplankton ratios in the Austin section indicate relative water depths or distance from shore, or both. Comparison of palynomorphs from other areas previously studied indicates that the Corsicana Marl and Kemp Clay, and comparable age strata of the Olmos and Escondido Formations, are probably about the same age as the Red Bank Formation of New Jersey and older than the Upper Moreno Formation of California.